In recent years, development of an electric automobile that uses a motor for traveling driven by electric power from a battery for traveling as a driving source or a hybrid car that uses an engine and a motor for traveling as a driving source is performed to replace an automobile that uses only an internal combustion engine (engine) as a driving source. In such an electric automobile or a hybrid vehicle as described above, similarly as in a case in which a driver grasps a remaining amount of fuel and suitably performs refueling in an automobile that only uses an engine as a driving source, it is necessary for a driver to grasp a remaining amount of a battery (remaining electric power amount of a battery) or a remaining amount of fuel and suitably perform battery charging and refueling. In this case, the remaining amount of the battery for traveling and the remaining amount of fuel are displayed on meters or the like to let the driver know the remaining amounts.
However, it is difficult for the driver to grasp an actual travelable distance from the displayed the remaining amount of the battery or the remaining amount of fuel on meters, and there is the possibility that the remaining amount of the battery or the fuel may be insufficient before arrival at a destination.
Therefore, a technology has been developed to make it possible that, in an electric automobile or a hybrid vehicle, not only a remaining amount of the battery and a remaining amount of fuel are simply detected and displayed but also a travelable distance (cruising distance) of the vehicle is estimated and indicated to the driver, or based on a travelable distance and a traveling distance to a destination, it is decided whether or not the vehicle can travel to the destination with the present remaining amount of the battery or the present remaining amount of fuel.
For example, Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 2010-226795) discloses a technology relating to calculation of a travelable distance in an electric automobile. In this technology, since the travelable distance with the present remaining amount of the battery varies according to an operation situation of an air conditioner, a travelable distance corresponding to a variation of the operation situation of the air conditioner is calculated. In other words, a voltage is multiplied by a current to calculate an electric power consumption amount of a motor generator, and a traveling distance in a predetermined period is divided by electric power consumption amount to calculate an electric power amount consumption ratio (namely, electric mileage). Then, a remaining amount of electric power is multiplied by electric power amount consumption ratio to calculate a travelable distance corresponding to a stopping state of the air conditioner. On the other hand, electric power consumption amount of the air conditioner is added to electric power consumption amount calculated by multiplying the voltage by the current to calculate a second electric power consumption amount. Then, the traveling distance in the predetermined period is divided by the second electric power consumption amount to calculate a second electric power amount consumption ratio corresponding to the operation state of the air conditioner, and then the remaining amount of electric power is multiplied by the second electric power amount consumption ratio to calculate a travelable distance corresponding to the operation state of the air conditioner.
Incidentally, in a hybrid vehicle, an optimum traveling mode is automatically selected in response to a driving state or a vehicle state. The traveling mode includes, for example, a mode called EV traveling mode in which the vehicle travels only with a motor for traveling and another mode called series traveling mode in which the vehicle travels only with a motor for traveling while generation of electric power is performed by an engine. Generally, when the EV traveling mode is selected, only electric power of a battery is used, whereas when the series traveling mode is selected, both of fuel in a fuel tank and electric power of a battery are used.
Therefore, if the electric mileage and the fuel mileage (value calculated by dividing a traveling distance in a predetermined period by a fuel consumption amount) are calculated without taking the traveling modes into consideration, it is possible that an error from an actual electric mileage and an actual fuel mileage may appear or a calculation load may increase. For example, since motor traveling in the EV traveling mode is performed without consuming fuel, when calculation of the fuel mileage is performed in the EV traveling mode, the fuel mileage is calculated to a better value than that of the actual fuel mileage, and the error from the actual fuel mileage increases and the accuracy of the calculation degrades. Further, in the series traveling mode, charging by engine electric power generation and discharging by the motor traveling are performed in parallel to each other in the battery. Therefore, the charging ratio of the battery constantly varies, and if a balance between charging and discharging is successively calculated, it is possible that the calculation load may become heavy.
If a calculation error in the electric mileage or the fuel mileage appears in such a manner as described above, an error also appears in calculation of a cruising distance of a hybrid vehicle and an erroneous cruising distance is indicated to the driver. The driver would grasp the indicated cruising distance and perform battery charging and refueling if the cruising distance decreases. For the decision of the charging and the refueling, the cruising distance is desired to be an accurate value and is required to be at least a surely travelable value.